rtpproxy: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On CentOS possible default full paths are:

/usr/bin/rtpproxy - from package: rtpproxy

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/bin/rtpproxy - from package: rtpproxy

You may install the required package with command apt-get install {package}

Error in other languages:
rtpproxy: bevel nie gevind nie
rtpproxy: comandă negăsită
rtpproxy: comando não encontrado
rtpproxy: commande introuvable
rtpproxy: command not found
rtpproxy: käsku ei ole
rtpproxy: không tìm thấy lệnh
rtpproxy: komanda nerasta
rtpproxy: Kommando nicht gefunden.
rtpproxy: kommandot finns inte
rtpproxy: komut yok
rtpproxy: nie znaleziono polecenia
rtpproxy: níor aimsíodh an t-ordú
rtpproxy: no se encontró la orden
rtpproxy: no s'ha trobat l'ordre
rtpproxy: opdracht niet gevonden
rtpproxy: parancs nem található
rtpproxy: perintah tidak ditemukan
rtpproxy: príkaz nenájdený
rtpproxy: příkaz nenalezen
rtpproxy: команда не найдена
rtpproxy: командата не е открита
rtpproxy: 命令找不到
rtpproxy: コマンドが見つかりません